Every step in technology is aimed at solving problems left in previous ages. That rule also applies in networking and computing fields. Just like PCIe, originally called PCI Express (peripheral component interconnect express), is an interface bus standard for connecting devices into equipment like computers, network servers, and Ethernet switches. The existence of this standard is to meet the needs for higher bandwidth, greater flexibility, and better performance of networking devices, which cannot be achieved by its predecessor PCI. Since its debut in 2001, PCIe has rapidly developed and widely applied in many network devices, especially for the network expansion card. In this post, PCIe-based cards, as well as how to choose a suitable PCIe card will be the focus.

What Is PCIe Card and How Does It Work?

As we mentioned before, PCIe is an interface type. Undoubtedly, the PCIe card refers to the network card with PCIe interface. Currently, in the market, network or Lan card, video or graphics card, sound card, and hard drive controller card are commonly seen PCIe cards. Specifically, PCIe-based expansion cards are existed to fit into PCIe based slots in the motherboard of devices like host, server, and network switch. After inserting, a logical connection will be formed between PCIe card and slot to communicate with each other. This connection, called an interconnect or link, enables a point-to-point communication channel between two PCIe ports, and allows both of them to send and receive ordinary PCI requests and interrupts. At the physical level, every PCIe slot contains one or more lanes. And each lane is composed of two different data transferring pairs, one pair for transmitting data and the other for receiving data. Therefore, each lane consists of four wires or signal traces.

Figure 1: How PCIe Card Works?

How Many Types of PCIe Cards Exist?

Based on different features, different types of PCIe card can be found in the market. Designed for different functions, there are network card, video card, etc. However, when looking at the PCIe card size and version, you will get other types. In the following part, PCI express card types will be uncovered according to PCIe card sizes and versions.

Based on PCIe Card Sizes

Figure 2: Comparison of Different PCIe Card Sizes

Generally, there are four commonly seen physical sizes in the market: x16, x8, x4, and x1. The number after the “x” refers to the number of lanes in the PCIe slot. For example, a PCIe x4 card means the card has four lanes. In applications, you will need to insert the PCIe card into a PCIe slot of a host or server with the same size and configurations of that card. However, confronted with cases like slot shortage, the PCIe card also can be fitted into a lot larger slot. For instance, you can place a PCIe x8 card into a PCIe x16 slot when the PCIe x8 slot has been occupied, but that card will always run in PCIe x8 mode. For more details about the PCIe card sizes, you can refer to the following table.

PCIe Slot Width

Number of Pins

Length

PCIe x1

18

25 mm

PCIe x4

32

39 mm

PCIe x8

49

56 mm

PCIe x16

82

89 mm

Based on PCIe Card Versions

Currently, there are four versions of PCIe card: PCIe 1.x, PCIe 2.x, PCIe 3.x, and PCIe 4.x. Each generation will double its bandwidth over the previous one. All PCIe card versions are backward and forward compatible. That is to say, any version of PCIe card and motherboard can work together in the mode of the lowest version. In the following table, a comparison of bandwidths among four typical PCIe versions has been listed for your better understanding.

Version

Bandwidth (per lane)

Bandwidth (per lane in an x16 slot)

PCIe 1.0

2 Gbit/s (250 MB/s)

32 Gbit/s (4000 MB/s)

PCIe 2.0

4 Gbit/s (500 MB/s)

64 Gbit/s (8000 MB/s)

PCIe 3.0

7.877 Gbit/s (984.625 MB/s)

126.032 Gbit/s (15754 MB/s)

PCIe 4.0

15.752 Gbit/s (1969 MB/s)

252.032 Gbit/s (31504 MB/s)

How to Select a Desirable PCIe Card?

Just like the types we have mentioned in the previous part, there are various types of PCIe cards in the market. It will be confusing to choose one. According to the features of PCIe cards as well as the FS IT experiences, we conclude some factors that you need to pay attention to.

Function: The first thing you need to do is to know what function you need to realize. PCIe card consists of a Lan card, graphics card, sound card, etc. They are used to connect different devices and achieve different functions.

PCIe Card Version and Slot Width: After nailing down the function, you need to know which PCIe version and slot width can be compatible with your current equipment and network environment.

Protocol Standard: To achieve different technologies, the corresponding protocol standards need to be supported by your card. Therefore, when you buy a PCIe card, you should know whether the card supports standards you need like RDMA, RoCE, ISCSI, and FCoE.

Chip: This is another common factor you need to care. Network cards applied for different functions have different chips. For video cards, chips from AMD and NVIDIA are used most. As for network adapter, chip from Intel, Cisco, Broadcom, and Mellanox are the trend.

Others: According to the PCIe card types, you may also need to take into account other factors. For example, when you choose a network adapter, you still need to consider the data rate and port number. There are many types of data rate and port number provided in the market. In FS, 10G/25G/40G network cards with single, dual, or quad port types are available for choice.

Figure 3: PCIe Network Adapters with Different Port Number

Conclusion

With a wide variety of PCIe card market, it’s confusing to select a desirable one. In this post, we make an exploration of PCIe-based card from its history and development to its applications. Hope this post will give you some inspirations in choosing the right PCIe card. By the way, if you plan to buy a PCIe network card, please feel free to contact FS sales.